Crop Sorghum Ensiled With Unsalable Vegetables Increases Silage Microbial Diversity

Abstract

Ensiling vegetables with forage crops is a suggested method of waste diversion and can be directly utilized as a livestock feed. Carrot or pumpkin, ensiled at 0, 20, or 40% dry matter (DM) with crop sorghum, and with or without a second-generation silage inoculant were assessed for nutritive composition, organic acid profiles, aerobic stability and <i>in vitro</i> rumen fermentation characteristics. The study was a completely randomized design, with the fixed effects consisting of vegetable type (carrot vs. pumpkin), level (i.e., the level of vegetables), inoculant (inoculant or non-inoculant) and the interactions, and mini-silos within treatment as the random effect. The experimental unit for sorghum treatments represented by each mini-silo (5 kg capacity). Silage was sampled after 70-days ensiling for nutrient composition, 14-day aerobic stability, organic acid profiles and microbial diversity. After 24 h <i>in vitro</i> incubation, rumen fermentation parameters were assessed, measuring gas and methane (CH₄) production, <i>in vitro</i> digestibility and volatile fatty acid concentrations. Sorghum ensiled with carrot or pumpkin at 20% or 40% DM increased crude fat (<i>P</i> ≤ 0.01) and decreased (<i>P</i> ≤ 0.01) silage surface temperature upon aerobic exposure compared to the control. Bacterial communities analyzed through 16S rRNA gene sequencing linearly increased (<i>P</i> ≤ 0.01) in diversity across both vegetables when the vegetable proportion was increased in the silage; dominated by <i>Lactobacillus</i> species. ITS analysis of the fungal microbiota upon silage opening and after 14 days (aerobic stability) identified increased (<i>P</i> ≤ 0.03) fungal diversity with increasing vegetable proportions, predominantly populated by <i>Fusarium denticulatum</i>, <i>Issatchenkia orientalis</i>, <i>Kazachstania humilis</i>, and <i>Monascus purpureus</i>. Upon assessment <i>in vitro</i>, there was an increase (<i>P</i> ≤ 0.04) in <i>in vitro</i> digestibility and some CH₄ parameters (% CH₄, and mg CH₄/g DM), with no effect (<i>P</i> ≥ 0.17) on remaining CH₄ parameters (mL CH₄/g DM, mg CH₄/g digested DM), gas production or pH. However, increasing vegetable amount decreased percentage of acetic acid and increased percentage of propionic acid of the total VFA, decreasing A:P ratio and total VFA concentration as a result (<i>P</i> ≤ 0.01). The results from this study indicate including carrot or pumpkin at 20 or 40% DM in a sorghum silage can produce a highly digestible, microbially diverse and energy-rich livestock feed.